The present invention relates to the field of treatment of heart disease. In particular, the present invention relates to an intravascular device, particularly suited for use for percutaneous transluminal treatment for heart disease.
A normal artery is composed of essentially, three layers, the intima, the media and the adventitia. The intima is the innermost layer of the artery. It is composed of a thin layer of endothelial cells that provide a smooth surface between the blood and an interior wall of the artery. The media is an intermediate layer which is separated from the intima by an internal elastic membrane, which allows material to diffuse through the intima and into the medial tissue. The media is a muscle layer composed of a network of smooth muscle cells. The smooth muscle cells of the media contract and relax to regulate vessel tone which in turn affects blood pressure and local blood flow. The outermost layer or adventitia is composed of a connective tissue and scattered smooth muscle cell bundles.
Atherosclerosis is a disease which affects a normal artery restricting the function of the artery. Atherosclerosis involves the gradual build up over time of atherocelerotic plaque or atheroma. Atherocelerotic plaque buildup begins in the intimal layer of the artery and progresses with the deposit of fatty debris from the blood through the endothelium. As the formation progresses, the endothelium becomes irregular and the artery constricts because of the build up of the plaque. The build up is so significant that the plaque now diminishes the effectiveness or area of the artery.
Balloon dilatation angioplasty has become recognized as an efficient and effective method for treating atherocelerotic buildup in coronary arteries. A dilatation balloon catheter is inserted preferably into the femoral artery of the patient and it is advanced to the obstructed area of the coronary artery. The balloon is inflated to compress the plaque against the artery wall and also to stretch the artery to dissect the plaque and open the artery thereby permitting an acceptable artery blood flow.
Before an angioplasty procedure is performed, radiography is used to survey the extent of damage or disease present in the artery. Dilatation balloon catheters are rated for different functions depending on the extent to which the artery is occluded or obstructed by plaque and the stage to which the atherocelrotic deterioration has progressed.
However, often times, the nature and extent of the damage is not apparent from the pre-angioplasty analysis and it is necessary to substitute the original balloon catheter inserted for an alternate sized balloon catheter. This process is generally referred to as a catheter exchange. A catheter exchange becomes a very arduous procedure if it is necessary to retrace the second catheter through the tortious anatomy (i.e., through a coronary artery) of a patient to position the balloon at the occluded area.
There are generally two type of balloon catheters, over-the-wire catheters and non-over-the wire-type catheters. In an over-the-wire catheter, the wire is slidably disposed within the catheter so that the catheter may be withdrawn independently of the wire, and the wire can remain in place to guide a substitute catheter to the treatment site. In a non-over-the-wire catheter the entire catheter is withdrawn during a catheter exchange so the tortious path to the treatment site must be retraced.
The condition of the patient may also be affected by thrombolytic buildup which can also occlude the lumen of the artery. Thrombolytic buildup results from platelet found in red blood cells which is thought to promote coagulation. In a healthy artery, endothohelial cells produce substances that inhibit platelet. Thus, there is a propensity for thrombolytic buildup at the diseased site in an artery. Further stagnation of the blood flow and platelet during angioplasty increases the risk of thrombolytic buildup.
Thrombolytic drugs and agents are generally used to dissolve the blood clot caused by the "build up" of platelet matter and to reverse the build up of the platelet matter. Alternatively, aspiration is another technique for treating thrombus "build up". It is important that the thrombolytic drugs or other treatment be administered before blood flow through the artery is completely or significantly restricted. Furthermore, thrombolytic drugs are generally extremely expensive so it is desirable that the drug be administered effectively and efficiently without waste.
Accordingly, it is important to be able to selectively provide a means for efficiently introducing a thrombolytic agent into the diseased artery during a balloon dilatation procedure. Also, if necessary it is desirable to be able to easily substitute one size catheter for a different size catheter if the original catheter inserted can not properly dilate the lesion.